With the rapid progress of semiconductor industries, the integrated circuits (ICs) used in electronic devices are developed toward minimization. high operating speed and increasing integration level. In a computer system or similar electronic products, CPU determines system performance, and the capacity and the operating speeds of the memory chips are important factors that affect data processing efficiency. Take a memory chip for example. Nowadays, for complying with a requirement of miniaturization, the memory chip is designed to have a high storage capacity with a reduced size. For a purpose of reducing cost and size, a so-called stacking method is widely used to interconnect multiple memory chips in a stack form so as to form a memory module, i.e. a stacked IC.
Referring to FIG. 1, a conventional stacked IC is shown. The stacked IC I comprises a first IC package unit 11 and a second IC package unit 12 in a stack form. The first IC package unit 11 and the second IC package unit 12 are provided on the bottom and the top of the stacked IC, respectively. Each of the IC package units 11 and 12 comprises an IC chip, a lead frame and a plurality of lead wires. In order to make electrical connection between these two IC package units 11 and 12, the lead wires 112 of the second IC package unit 12 should be bent inward to be in contact with the lead wires 111 of the first IC package unit 11 and then soldered thereon. Although the manner for fabricating this stacked IC 1 is cost effective, the internal structure of the second IC package unit 12 may be damaged during the operation of bending the lead wires 112. In addition, such manner is time-consuming.
Referring to FIG. 2, another conventional stacked IC is shown. The stacked IC 2 comprises a first IC package unit 21, a second IC package unit 22 and an interface layer 23 sandwiched between the IC package units 21 and 22. Each of the IC package units 21 and 22 comprises an IC chip, a lead frame and a plurality of lead wires. The interface layer 23 having a plurality of bent pins 231 extending from the bilateral edges thereof. In order to make electrical connection between these two IC package units 21 and 22, the lead wires 212 of the second IC package unit 22 is firstly soldered onto the interface layer 23. The bent pins 231 of the interface layer 23 are then soldered onto the lead wires 211 of the first IC package unit 21 so as to form the stacked IC 2. The manner for fabricating this stacked IC 2 is more complicated because the pins 231 of the interface layer 23 need to be bent in advance and the soldering procedure should be done manually.
Referring to FIG. 3, another conventional stacked IC is shown. The stacked IC 3 comprises a first IC package unit 31 and a second package unit 32. Each of the IC package units 31 and 32 comprises a chip, a lead frame and a plurality of lead wires. Each terminal of the lead wires 311 and 322 for the respective IC package units 31 and 32 is connected to a conductor 33, 34. The connection of the conductors 33 and 34 performs the electrical connection between these two IC package units 31 and 32. The manner for fabricating this stacked IC 3 uses no interface layer. However, this manner is more time-consuming and costly because two stages are required to make electrical connection, i.e. (1) the conductors should be coupled to the terminals of the lead wires, and (2) these conductors are further connected with each other.